Once you do this, the contacts will sync to the selected Google account. Now, whenever you buy a new Android smartphone, just sign in with the Google Account that you used for syncing the data on your older device, and in a few seconds, your contacts will show up on the new Android smartphone. It is that simple.
Now, once again, there are a few apps that claim to assist you with this whole data migration, and while some of them do work, our frank assessment is that they are not necessary. The Android platform is powerful and is more than capable of handling such tasks without assistance.
